Retrospective Study for Diagnosis of Undetected IgG4 Related Diseases in Patients With High Serum IgG4 Levels.

Immunoglobulin G4-related disease (IgG4-RD) is an increasingly recognized syndrome of unknown etiology comprised of a collection of disorders that share specific pathologic, serologic, and clinical features. Histopathological analysis of biopsy specimens remains the cornerstone in the diagnosis of IgG4- related disease. Elevated concentrations of IgG4 in tissue and serum are helpful in diagnosing IgG4-related disease, but neither one is a specific diagnostic marker. Correlation with specific histopathological findings is essential, regardless of the serum IgG4 concentration, the number of IgG4-positive plasma cells in tissue, or the ratio of IgG4 to IgG in tissue. Misdiagnoses of IgG4-related disease are increasingly common because of excessive emphasis on moderate elevations of serum IgG4 concentration and overreliance on the finding of IgG4-positive plasma cells in tissue.